Such a process is known from Kirk Othmer, Encyclopedia of Chemical Technology, Vol. 8 (1993), pp. 672-753. Described herein is the dying of plastic fibres in a bath containing a solution of a dye, in which the dye, in this case the active substance, penetrates the fibre.
A drawback of the known process is that the active substance is with difficulty absorbed into the plastic. It is for example not really possible to dye polypropylene fibres because the dye does not, or only with great difficulty, penetrates the polypropylene fibre.
The aim of the invention is to provide a process that does not possess the aforementioned drawback.